EGUsphere EGUsphere EGUsphere EGUsphere Copernicus Publications Göttingen, Germany 10.5194/egusphere-2025-1544 Modeling the mechanisms of coastal vegetation dynamics and ecosystem responses to changing water levels Ding Junyan https://orcid.org/0000-0002-0739-0545 1 McDowell Nate 2 3 Bailey Vanessa 2 Conroy Nate https://orcid.org/0000-0003-0597-3373 4 Day Donnie J. https://orcid.org/0000-0001-9454-7602 5 Fang Yilin https://orcid.org/0000-0003-1969-9889 6 Kemner Kenneth M. 7 Kirwan Matthew L. 8 Koven Charlie D. https://orcid.org/0000-0002-3367-0065 9 Kovach Matthew 5 Megonigal Patrick https://orcid.org/0000-0002-2018-7883 10 Morris Kendalynn A. 11 O’Meara Teri 12 Pennington Stephanie C. https://orcid.org/0000-0003-2685-1092 11 Peixoto Roberta B. 5 Thornton Peter https://orcid.org/0000-0002-4759-5158 12 Weintraub Mike https://orcid.org/0000-0002-9623-2855 5 Regier Peter 13 Sandoval Leticia 5 Machado-Silva Fausto 5 Stearns Alice https://orcid.org/0009-0005-7628-3419 10 Ward Nick https://orcid.org/0000-0001-6174-5581 13 Wilson Stephanie J. https://orcid.org/0000-0002-5484-0748 10 Department of Biology, Occidental College, Los Angeles, CA, USA, 90041 Biological Science Division, Pacific Northwest National Laboratory, Richland, WA, USA, 99352 School of Biological Sciences, Washington State University, PO Box 644236, Pullman, WA, USA, 99164-4236 Earth and Environmental Sciences Division, Los Alamos National Laboratory, New Mexico, USA, 87545 The University of Toledo, Toledo, OH, USA, 43606 Earth Systems Science Division, Pacific Northwest National Laboratory, Richland, WA, USA, 99352 Molecular Environmental Sciences Group, Argonne National Laboratory, Lemont, IL, USA 60439 Virginia Institute of Marine Science, College of William and Mary, Gloucester Point, VA, USA, 23062 Climate and Ecosystem Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, USA Smithsonian Environmental Research Center, Edgewater, MD, USA, 21037 Joint Global Change Research Institute, Pacific Northwest National Laboratory, College Park, MD, USA, 20740 Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA, 37830 Marine and Coastal Research Laboratory, Pacific Northwest National Laboratory, Sequim, WA, USA, 98382 25 04 2025 2025 1 31 Copyright: © 2025 Junyan Ding et al. 2025 This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/4.0/ This article is available from https://egusphere.copernicus.org/preprints/2025/egusphere-2025-1544/ The full text article is available as a PDF file from https://egusphere.copernicus.org/preprints/2025/egusphere-2025-1544/egusphere-2025-1544.pdf

Coastal forests are increasingly experiencing mortality due to inundation by fresh- and seawater, leading to their replacement by marshes. These shifts alter vegetation composition, biogeochemical cycling, carbon storage, and hydrology. Using a hydraulically enabled ecosystem demography model (FATES-Hydro), we conducted numerical experiments to investigate the mechanisms behind inundation-driven forest loss and the ecosystem-scale consequences of forest-to-marsh transitions. We compared mortality processes and their effects across broadleaf and conifer trees at two coastal sites&mdash;Lake Erie (freshwater) and Chesapeake Bay (saline).</p> <p>Our simulations show that hydraulic failure, driven by root loss under prolonged flooding, is the primary mortality mechanism across both tree types and sites. Forest replacement by marsh reduced ecosystem-scale leaf area index (LAI), gross primary production (GPP), transpiration, and deep soil water uptake in conifer forests, while broadleaf forests experienced smaller changes due to lower initial LAI and greater marsh compensation. Marsh invasion occurred following canopy thinning driven by tree mortality. These findings suggest that, under similar root loss, hydraulic failure dominates coastal tree mortality regardless of species or water type, with denser forests experiencing stronger ecosystem impacts. Our study identifies key mortality mechanisms and offers testable hypotheses for future empirical studies on coastal vegetation change.

 U.S. Department of Energy 2012671 National Science Foundation 1654374 1832221 2012670